In the wireless communication system, the transmitting terminal usually implements transmissions by the maximum power in order that the transmission apparatus could transmit packets as far as possible. However, when there is a rather short distance between the receiving terminal and the transmitting terminal, the packet transmission which the transmitting terminal implements by the maximum power would result in the wasted power, and at the same time, it is possible that the packet could not be correctly received owing to the saturation or clipping of the signals received by the receiving terminal. Therefore, if the distance between the transmitting terminal and the receiving terminal could be correctly calculated, the transmission power at the transmitting terminal could be adaptively changed, so that the transmitting terminal could achieve the same or even better transmission efficiency by less power.
There has been such one method that the signal strength of the packet received by the transmitting terminal is used to judge the distance between the transmitting terminal and the receiving terminal. However, an incorrect judgment would possibly occur if the distance is judged according to the signal strength. This is because, in the air, either the refraction, reflection, or diffraction of a signal would result in the signal fading, which would result in the decreasing signal strength or the increasing bit error rate of the packet received by the transmitting terminal. For example, when there is the low strength of the signal received by the transmitting terminal, the transmitting terminal would judge that it is relatively far from the receiving terminal. As a result, the transmitting terminal would transmit the packet by a higher transmission power, which would result in a wasted transmission power. Instead, when there is the high strength of the signal received by the transmitting terminal, the transmitting terminal would judge that it is relatively close to the receiving terminal. As a result, the transmitting terminal would transmit the packet by a lower transmission power, and therefore the receiving terminal could not receive the packet. Thus, in a certain situation, it is inappropriate to determine the distance between the transmitting terminal and the receiving terminal based on the signal strength.